In wireless communication systems, such as WiMAX, a Mobile Station (MS) may enter an Idle Mode when it is not actively exchanging user data with the Base Station (BS). In Idle Mode, the MS may conserve battery power by turning off its transmitter and turning on its receiver only during predetermined times, when the BS may notify the MS of pending traffic using a Paging procedure. While an MS is in Idle Mode, one BS will serve as its Selected BS. The MS synchronizes to the Selected BS, acquires its operational and configuration parameters, and monitors its transmissions for Paging notifications during predetermined times. As a MS moves through a network, it may choose a new Selected BS based on its signal strength relative to other BSs. Selecting a new Selected BS does not require the MS to exchange messages with the network.
As the MS moves, it may use a Location Update procedure to inform the network of its location so that paging notifications can be delivered to its Selected BS. When the MS performs the Location Update procedure, it exchanges messages with the network so, considering battery power consumption, it is beneficial if the MS does not update its location every time it selects a new BS. Rather, BSs may be grouped according to their proximity to each other and the MS updates its location only when it selects a BS in a different group than the current Selected BS. This means that the MS's location is not tracked with a granularity of a single BS so multiple BSs (i.e., BSs in the same group) must transmit Paging notifications for the same MS.
In WiMAX, this capability is provided by grouping BSs into Paging Groups, which are identified with a Paging Group Identifier (PGID). Each BS includes the PGIDs that it supports in its broadcast configuration information and when an MS performs the Location Update procedure, it is assigned a Paging Group that the newly selected BS supports. Each BS that supports this Paging Group will transmit Paging Notifications for this MS so the MS only updates its location when it selects a BS that is not a member of its assigned Paging Group.
When BSs are mobile, additional considerations should be made to make the Paging/Location Update processes efficient. To illustrate, when a mobile BS is near an MS for a short period of time, the MS may select it and perform Location Update if the mobile BS does not support the MS's current Paging Group. When the mobile BS then moves away from the MS, the MS may need to select another BS and perform another Location Update. In an area with many mobile BSs, the MS may perform multiple Location Updates in a short period of time, which wastes battery power and radio resources.
An example of a mobile BS is a Mobile Relay Station (MRS). Relay Stations (RSs) are of considerable interest in the wireless industry due, for instance, to the anticipated deployment of wireless networks capable of supporting higher data rates and, consequently, applications requiring higher bandwidth, such as media-rich applications. When the new networks are deployed using legacy cells plans, the higher data rates required for the higher-bandwidth applications can not be supported at the edge of the cell, which effectively reduces the size of the cell. RSs may be deployed in an area of good BS coverage and serve MSs in areas of weak BS coverage by relaying data between the BS and the MSs.
RSs may also be deployed to mitigate coverage holes, such as Mobile RSs (MRSs) on trains, for example. In this type of case, additional considerations may be made regarding selection of the MRS and Location Updates when an MRS is near an MS, such as whether MS does or does not join the MRS. As an example, an MS has joined an MRS when its movement is correlated to the MRS movement, such as when a MS user boards a train with an MRS.
Using the current methods in IEEE 802.16 Multi-hop Relay task group (802.16j), it is possible to avoid multiple Location Updates when an MRS is near an MS, the MS selects the MRS, and then the MRS moves (away from the MS). To do this, the MRS supports its own unique Paging Group as well as the Paging Group of its parent BS, for example, a BS at a train station. If an MS's Selected BS is the MRS's parent BS, then when the MRS moves near the MS, the MS may select it due to its signal strength. The MS will not perform Location Update, however, because the MRS supports the MS's Paging Group (Paging Group of MRS's parent BS). When the MRS moves and the MS has not joined the MRS, the MS will select the BS again, but will not perform Location Update since it is still assigned the Paging Group of this BS. If the MS joins the MRS, it would continue to have the same Paging Group assignment (associated with the parent BS).
When the MRS hands over to a new BS, it will then support the (new) Paging Group for this new BS. It may also discontinue supporting the Paging Group of its previous BS, which will cause the MS to perform Location Update. At this time the MS should be assigned the Paging Group of the MRS so that it does not need to update its location when the MRS hands over to a new BS. When the MRS changes its supported Paging Groups, its broadcast configuration information changes and MSs being served by the MRS are required to update their stored configuration for the MRS, which interrupts their idle/sleep cycle and impacts battery power consumption.